1. Field of the Invention
The present invention relates to a corneal surgery apparatus for correcting a refractive error of a patient""s eye by ablating a cornea of the patient""s eye with a laser beam.
2. Description of Related Art
It has been known that a laser corneal surgery apparatus for ablating a cornea of a patient""s eye with an excimer laser beam is used to change a refractive power of the cornea for correcting a refractive error such as myopia, hyperopia, astigmatism, and the like. For such a keratorefractive surgery, PRK (photorefractive keratectomy) and LASIK (laser assisted in-situ keratomileusis) are usually carried out. In PRK, a laser beam is irradiated after peeling an epithelium off, and in LASIK, a laser beam is irradiated to ablate a corneal stroma after a flap is formed by incising the part from the epithelium up to the corneal stroma in a layered form, where the flap is replaced after the irradiation.
Also, as to a keratorefractive surgery performed by this type of the apparatus, an ablation amount of a cornea is determined from the data for correcting a refractive error such as a corneal shape which is obtained before an operation, refractive power to be corrected, and a size of an optical zone, and then a laser beam is irradiated in accordance with the determined ablation amount. And, a corneal shape is generally measured with an apparatus in which a placido ring target is projected on a cornea to detect a mirror surface reflected image on the cornea. Such a measurement apparatus is separated from a surgery apparatus.
However, measurement of the corneal shape by using the mirror surface reflected image is incapable of measuring the corneal shape just before laser irradiation (after the epithelium is peeled off in PRK, and after the flap is formed in LASIK) and soon after laser irradiation. Accordingly, it is impossible to know whether the cornea is ablated in accordance with the determined ablation amount. Therefore, measurement of refractive power before and after the operation is conventionally conducted to judge whether the operation is successful. When the desired correction has not been made, another operation is performed after the eye of the patient heals. This is a burden to the patient.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a corneal surgery apparatus with which an operation can be performed more precisely with improved accuracy in correcting a refractive error by keratectomy.
To achieve the objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, a corneal surgery apparatus ablating a cornea with a laser beam comprises ablation amount computing means for obtaining an ablation amount of the cornea for each of plural ablation steps based on a refractive error of an eye to be operated, determining means for determining laser irradiation control data for each of the ablation steps based on the ablation amount for each of the ablation steps obtained by the ablation amount computing means, corneal shape measurement means including a projecting optical system for projecting a target for measuring a corneal shape on the cornea, a photographing optical system for photographing an image of corneal reflection of the target projected on the cornea, and shape computing means for obtaining a corneal shape by processing the photographed target image, and correcting means for comparing a predetermined ablation amount with an actual ablation amount for a certain ablation step based on the corneal shape measured after laser irradiation at the ablation step and for correcting the laser irradiation control data for a next ablation step based on a result of the comparison.
In another aspect of the present invention, a corneal surgery apparatus ablating a cornea with a laser beam comprises a laser source emitting a laser beam, an irradiation optical system for irradiating the laser beam emitted from the laser source on the cornea, a projecting optical system having a light source and a target plate, for projecting a target for measuring a corneal shape on the cornea, a photographing optical system having a photographic element, for photographing an image of corneal reflection of the target projected on the cornea, a first computing unit which obtains a corneal shape by processing the photographed target image, a second computing unit which obtains an ablation amount of the cornea for each of plural ablation steps based on a refractive error of an eye to be operated, determines laser irradiation control data for each of the ablation steps based on the ablation amount of each of the ablation steps, further compares a predetermined ablation amount with an actual ablation amount for a certain ablation step based on the corneal shape obtained after the laser irradiation at the ablation step, and corrects the laser irradiation control data for a next ablation step based on a result of the comparison, and control unit which controls the irradiation optical system based on the determined laser irradiation control data and the corrected laser irradiation control data.
Yet, in another aspect of the present invention, a corneal surgery apparatus ablating a cornea with a laser beam comprises a laser source emitting the laser beam, an irradiation optical system for irradiating the emitted laser beam on the cornea, a projecting optical system having a light source and a target plate on which a slit is formed, for projecting a slit-shaped target for alignment on the cornea to perform alignment of the apparatus in a direction related to a distance to the cornea, a moving unit which moves the projecting optical system in the direction related to the distance to the cornea at a specified step, a photographing optical system for photographing an image of corneal reflection of the target projected on the cornea, a detecting unit which detects an alignment condition in the direction related to the distance to the cornea by processing the photographed target image, and a computing unit which obtains a corneal shape by processing the photographed target image.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.